In mammals the nervous system is functionally divided into a somatic nervous system and an autonomic nervous system. The autonomic nervous system functions automatically and reflectory. The autonomic nervous system can further be divided into the counteracting sympathetic and parasympathetic systems. The sympathetic and parasympathetic nerves have opposite effects.
The sympathetic nervous system mobilizes the resources in the organism in a so-called “stress phase” such that an immediate dangerous situation/a challenge is handled in the optimum manner. This means that mentally the person thinks faster and more clearly at the same time as sharpening the ability to focus his/her thoughts. For supporting this purpose, irrelevant sense impressions are effectively impeded. Physically the body responds by lowering the response time, increasing the muscle strength, sharpening the senses, and optimizing the coordination between thought and motor skills.
In conclusion, the above entails that the “stress phase” is a positive physiological phenomenon, when it manifests itself in the right amount and in the right balance with the necessary recovery, which as described below is effected when the parasympathetic nervous system dominates.
The parasympathetic nervous system restores and builds up the organism's resources and thereby ensures that the necessary resources are available when they are to be mobilized in an acute stress situation.
Physiologically, simulation via the sympathetic nerves increases the pulse and the blood pressure and inhibits the secretion formation in the glands, etc., whereas the parasympathetic nerves inter alia lower the heart rate and the blood pressure and stimulate glands to secrete. During stress and in dangerous situations the sympathetic nervous system is activated.
Stress is a condition in which the resources of the organism are activated with a view to handling a situation which is perceived as dangerous or potentially dangerous by the brain. If the person has the necessary resources available, the situation is perceived in a positive manner. If the situation represents a state in which the strain exceeds the resources of the body, the organism's resources become taxed and longterm and intense stress will impair the person's performance. This state is called chronic or negative stress.
In its mildest form chronic stress manifests itself as moderate bodily symptoms such as muscle tension, fatigue or headache. In a more severe degree of stress additional symptoms are experienced in form of for instance memory problems, lack of concentration and distress from the internal organs (eg. palpitations, stomach ache, decreased libido). In an even more serious stress state, social ability is also impaired, eg reduced tolerance, irritability and uncontrolled bursts of anger. In the latter case, untreated chronic stress may lead to illness whereby the working capacity is lost for a period of time.
The body's reaction to the above strain is controlled by the hypothalamic-pituitary-adrenal system which activates the release of steroid hormones (glycocorticoids½) including cortisol. Additionally, other hormones are released among others catecholamines including dopamine, noradrenaline and adrenaline. As a result, a set of physiological reactions are created which in combination is called the response phase. Substantially all the systems of the body are affected including the brain, the cardiovascular system, the immune system, the respiratory system and the digestive system.
When the physical and mental dangers/challenges/strains have passed, the body's response thereto is inactivated and the recovery phase begins.
The stress reactions are not activated by purely physical or psychological threats, but also by our thoughts. A number of everyday-life situations inter alia rush for time, worries, personal relationship problems and financial worries, activates the response phase without the person being threatened. It is the accumulated effect of these minor but daily strains that lead to chronic stress.
As a part of avoiding that the stress condition develops and thus leads to negative implications, the determination of a person's acute or accumulated stress level is vital to allow for actions to be initiated which can reduce or completely remove the strains causing the stress or the person's readiness to handle these strains can be increased such that the negative stress-related consequences—both personal and social—may be averted and/or prevented. Stress cannot per se be considered an illness, but accumulated stress can make a person more susceptible to impacts which may develop into an illness.
A number of methods are known for determining the sympathetic tone (the activity of the sympathetic nervous system) as a measure of a person's stress level including measuring of cortisol in saliva, measuring of catecholamines (adrenaline and/or noradrenaline) and cortisol in serum as well as measuring of catecholamines in urine (Ekman R. and Lindstedt. G.: “Molekyler på liv og død” (molecules in life and death), in Ekman R. and Arnetz B. (red) “Stress; Molekyleme, Individen, Organisationen, Samhället” (stress; molecules, the individual, organisation and society), Libers publishing firm, Stockholm 2002, pages 77-89; Hansen A. M., Garde A. H., Christensen J. M., Eller N. H. & Nettestrøm B. “Evaluation of a radioimmunoassay and establishment of a reference interval for salivary cortisol in healthy subjects in Denmark”, Scand J Lab Invest 2003; 63: 303-10.) “Måling af hudtemperatur” (measurement of skin temperature) (Normell L A, Wallin B G. “Sympathetic skin nerve activity and skin temperature changes in man”. Acta Physiol Scand 1974; 91: 417-26) and sweat secretion are other known method for measuring stress.
The known methods of determining stress and sympathetic tone are encumbered by the drawbacks that either complicated technical analyses involving delays, communication and expenses are required or the methods are not unsusceptible to impacts/influences from the physical environment. Serum determination of for instance cortisol requires a laboratory analysis. Additionally one drawback of such a determination is that a change in the serum concentration of cortisol may rely on other causes than an increased level of stress. The sweat secretion determination is encumbered by the drawback that this determination may be highly unreliable, especially on a hot day where sweat secretion increases regardless of the person's level of stress.
A need thus exists for a fast, reliable and inexpensive method of determining the sympathetic tone as a measure of a person's potential to perform optimally both physically and mentally.